Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Safety laminates have been in commercial production for almost a century and have been utilized in applications that require sheet material having a high degree of clarity and impact resistance. For example, safety laminates have been widely used in the automobile industry as windshields or side windows because the laminate structures are characterized by high impact and penetration resistance and because they do not scatter glass shards and debris when shattered. More recently, safety laminates have also been incorporated into building structures as window, walls, stairs, etc.
Simple safety laminates typically consist of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric sheet. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets made of polycarbonate. Safety glass laminates have further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric sheets.
The interlayers used in safety laminates are typically made from relatively thick polymer sheets, which exhibit toughness and bondability to the glass in the event of a crack or crash. Widely used interlayer materials include complex, multicomponent compositions based on poly(vinyl butyral), poly(urethane), and ethylene vinyl acetate copolymers.
Ionomers are copolymers produced by partially or fully neutralizing the carboxylic acid groups of precursor or parent polymers that are acid copolymers comprising copolymerized residues of α-olefins and α,β-ethylenically unsaturated carboxylic acids. The use of ionomer interlayer sheets in safety laminates is known. See, for example, U.S. Pat. Nos. 3,344,014; 3,762,988; 4,663,228; 4,668,574; 4,799,346; 5,759,698; 5,763,062; 5,895,721; 6,150,028; 6,265,054; and 6,432,522, U.S. Patent Appln. Publn. Nos. 20020155302; 20060182983; 20070092706; 20070122633; 20070289693; 20080044666, and PCT Patent Appln. Publn. Nos. WO9958334; WO2006057771; and WO2007149082.
In this connection, ionomers have been useful in safety laminates intended for structures requiring a high degree of penetration resistance. Some examples include hurricane-resistant glazing and structural elements such as glass staircases and glass balustrades. In particularly demanding application, the use of ionomeric interlayer sheets in safety laminates having ballistic resistance is described in, e.g., U.S. Pat. No. 5,002,820 and PCT Patent Appln. Publn. No. WO03068501.
One way to improve ballistic resistance of a safety laminate is to increase the number of laminate layers or the thickness of the laminate layers. As the total thickness of the interlayer material in a safety laminate increases, any deficiency in the material's optical properties, such as haze, for example, increases in significance. These deficiencies may be exacerbated by the slower cooling rates typical of thicker safety laminates, which are more conducive to the formation of crystals.
Accordingly, there is a need to develop an ionomer composition that is useful in safety laminates and that is capable of retaining good optical properties when used at greater thicknesses, or when the manufacturing process requires slower cooling conditions.